30 SIDNEY P. HARMBR. 



A method of reproduction similar to the last is recorded by 

 Bigelow (4) ia Cassiopea xamachana. 



In Oceania armata, MetschnikoflF (24) characterises the 

 process of segmentation as a regular " Blastomerenanarchie " 

 (p. 38). The first two blastomeres almost separate from one 

 another ; while, in some cases, when the very slight connection 

 which normally exists between them becomes ruptured, the 

 separated blastomeres atrophy. Oceania further distin- 

 guishes itself, at the eight-cell stage also,'from other Medusse 

 investigated by Metschnikoff; the blastomeres, instead of 

 being arranged in an orderly manner, lying together " ganz 

 unregelmassig." This extraordinary irregularity (see Metsch- 

 nikoflp's pi. i, figs. 33—35) is equally remarkable at later 

 stages, and ultimately gives rise to irregularly shaped masses 

 of cells ; the embryos often assuming a quite " abenteuerliche 

 Gestaltj" due to the fact that they multiply by divi- 

 sion. Those embryos which do not divide form much larger 

 larvse than the others. 



As a converse to this may be mentioned some most interest- 

 ing results arrived at by Driesch (9) and by Fiedler (10). 

 Driesch showed that by violent shaking of the water contain- 

 ing Echinus-eggs which had divided into two blastomeres, 

 or in other ways, the two cells could be isolated from one 

 another. Each segmented in the same way that it would have 

 followed if it had remained connected with its fellow, i. e it 

 developed into a half-embryo, right or left as the case might 

 be. The segmentation cavity, at first widely open, closed up 

 in course of time so as to foi'm a blastophere, consisting (as 

 appeared from measuring the cells) of half the normal number 

 of cells, and being half the normal size. Three of these 

 embryos developed into complete Plutei, which differed from 

 normal ones only in size. In cases where the two original 

 blastomeres had been only partially separated, seventeen cases 

 were recorded in which the embryo distinctly consisted, at the 

 end of the first day, of two halves. In several cases each of 

 these embryos divided into two complete embryos, some of 

 which were shown to develop into small normal Plutei. In 



